Alzheimer disease: DNA fragmentation indicates increased neuronal vulnerability, but not apoptosis

Cytoplasmic cytochrome c immunolabelling in dystrophic neurites in Alzheimer's disease

Cytochrome c has a well-established role in electron transfer and as a mediator of apoptotic cell death. The cortical and intracellular localisation of cytochrome c immunoreactivity was examined in Alzheimer's disease and control cases. No differences in the cortical labelling pattern or the density of cytochrome c-positive cells in neocortical layer V were present between control and Alzheimer's disease cases. Punctate cytochrome c labelling was present in a subset of neocortical neurons, including clusters of intensely labelled pyramidal neurons that were not specifically associated with beta-amyloid plaques. With respect to Alzheimer's disease associated pathology, only 6.7 +/- 1.4% of neurons showing neurofibrillary tangle formation demonstrated punctate cytochrome c immunoreactivity. These results suggest that cytochrome c may label a subset of pyramidal neurons that is susceptible, yet relatively resistant, to Alzheimer's disease pathology. A low percentage of neurofilament triplet protein medium, tau and chromogranin A labelled dystrophic neurites were also cytochrome c-positive. There was also a trend towards an increase in the percentage of cytochrome c immunoreactive dystrophic neurites in pathologically aged control cases compared to Alzheimer's disease cases, suggesting that cytochrome c may be an early and transient epitope within dystrophic neurites. In contrast to the punctate cytochrome c labelling observed in cortical cells, cytoplasmic cytochrome c labelling was observed within dystrophic neurites. Although cytochrome c release is indicative of the activation of the intrinsic apoptotic pathway, cytoplasmic cytochrome c may also indicate mitochondrial damage or dysfunction.

Formation of phospho-SAPK/JNK granules in the hippocampus is an early event in Alzheimer disease

The mitogen-activated protein (MAP) kinase SAPK/JNK phosphorylates tau protein at many of its proline-directed serine/threonine residues in vitro and is a likely candidate kinase to phosphorylate the pathologically relevant S422 site on tau. Since phosphorylation of tau, particularly at S422, is a relatively early marker of AD and seems to precede tangle formation, it appears likely that an early form of activated SAPK/JNK might be detected by immunohistochemical means around the time that tau begins to aggregate into tangles. We report here that an antibody to phospho-SAPK/JNK (p-SAPK/JNK) reacts with several types of lesions including granular bodies in limbic areas; NFTs in limbic cortex and temporal neocortex; occasional neuritic plaques in temporal neocortex; and select axons in the hippocampus, entorhinal cortex, and inferior temporal cortex. In order to characterize the appearance of granular p-SAPK/JNK and determine if it appears early in disease, we employed an immunohistochemical study of postmortem limbic tissue from 20 cases ranging from Braak stages I-VI. By co-staining with anti-tau antibodies specific to different molecular events that occur during tangle evolution, we were able to identify the appearance of p-SAPK/JNK in early Braak stages with an increased elevation during the limbic stages of AD and during the early stages of the formation of individual hippocampal tangles.

Caspase-3 cleaved spectrin colocalizes with neurofilament-immunoreactive neurons in Alzheimer's disease

Corticocortical disconnection in Alzheimer's disease occurs by the progressive impairment and eventual loss of a small subset of pyramidal neurons in layers III and V of association areas of the neocortex. These neurons exhibit large somatic size, extensive dendritic arborization and high levels of nonphosphorylated neurofilaments of medium and high molecular weight that can be identified using a monoclonal SMI-32 antibody. It is thought that the accumulation of amyloid Abeta and neurofibrillary tangles may provoke metabolic disturbances that result in the loss of these SMI-32 immunoreactive neurons. The recent detection of increased levels of caspase-3 cleaved fodrin in frontal, temporal and parietal association areas in Alzheimer's disease brains suggests that programmed cell death may contribute to the destruction of SMI-32 positive neurons. In the present study, we utilized an antibody that selectively recognizes the 120 kDa breakdown product of alphaIIspectrin (fodrin) generated by caspase-3 to determine whether this protease is activated in vulnerable pyramidal neurons located in layers III and V of Alzheimer's disease brains. Neurons immunoreactive for caspase-3 cleaved alphaIIspectrin were located predominantly in layers III and V of the inferior frontal and superior temporal cortices of patients with Alzheimer's disease but not age-matched controls. Pyramidal neurons immunoreactive for caspase-3 cleaved alphaIIspectrin invariably displayed SMI-32 immunoreactivity suggesting that caspase-3 activation is a pathological event that may be responsible for the loss of a subset of pyramidal neurons that comprise corticocortical projections.

DNA end joining activity is reduced in Alzheimer's disease

Evidence indicates that oxidative stress-induced damage to DNA, protein, and other cellular components contributes to the progression of Alzheimer's disease (AD). Several studies indicate that postmitotic neurons have a reduced capacity for some types of DNA repair, which is further compromised by aging. Thus in AD, the cellular response to increased oxidative DNA damage may be inadequate to protect the genome. Mammalian cells use several mechanisms to repair DNA damage generated during normal oxidative metabolism or by genotoxic insults. The predominant mechanism to repair double strand breaks is non-homologous end joining (NHEJ) which utilizes the DNA-dependent protein kinase (DNA-PK) complex. A cell-free DNA end joining assay was employed to determine if NHEJ was reduced in nuclear cortical extracts from brains of AD versus normal subjects. This report demonstrates that end joining activity and protein levels of DNA-PK catalytic subunit are significantly lower in AD brains compared to normal controls. The amount of end joining activity correlates with the expression of DNA-PK and is dependent on DNA-PK catalytic activity. This indicates that repair of DNA double-strand breaks by the DNA-PK-dependent NHEJ pathway may be deficient in AD.

Mechanisms of cell death in neurodegenerative diseases: fashion, fiction, and facts

Apoptosis has become a most popular concept of cell death. However, the term is now so widely used and employed in such general terms in relation to neurological diseases that its application is very problematic. In addition, with the exception of developmental conditions, there is essentially no evidence of apoptosis fulfilling the criteria of its classical definition in any of the important human neurodegenerative diseases, including Alzheimer's, Parkinson's, Huntington's, Amyotrophic Lateral Sclerosis, and Creutzfeldt-Jakob disease. Importantly, a number of new cell death forms have been described in the literature and there is good reason to pay attention to these emerging concepts as they may provide a rationale for the development of disease-specific therapies.

Phosphorylated protein kinases associated with neuronal and glial tau deposits in argyrophilic grain disease

Tau phosphorylation was examined in argyrophilic grain disease (AGD) by using the phosphospecific tau antibodies Thr181, Ser202, Ser214, Ser 396 and Ser422, and antibodies to non-phosphorylated and phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinases (ERK), stress-activated kinase (SAPK), c-Jun N-terminal kinase (JNK), p38 kinase (p-38), alpha-calcium/calmodulin-dependent kinase II (alphaCaM kinase II), and glycogen synthase kinase-3 (GSK-3), all of which regulate phosphorylation at specific sites of tau. This is the first study in which the role of protein kinases in tau phosphorylation has been examined in AGD. Hyperphosphorylated tau accumulated in grains and pre-tangles in the hippocampus, dentate gyrus, entorhinal and trans-entorhinal cortices, and amygdala in all cases. Ballooned neurons in the amygdala, entorhinal, insular and cingulate cortex, and claustrum contained alphaB-crystallyn and phosphorylated neurofilament epitopes. Some astrocytes and scattered oligodendrocytes containing coiled bodies were recognized with anti-tau antibodies. A few tangles were observed in the entorhinal cortex and hippocampus corresponding to Alzheimer's disease (AD) stages I-III of Braak and Braak. None of the present cases was associated with progressive supranuclear palsy or with alpha-synuclein pathology. Two bands of phospho-tau of 64 and 68 kDa were observed in Western blots of sarkosyl-insoluble fractions enriched with abnormal filaments in AGD, a pattern that contrasts with the 4-band pattern obtained in AD. No modifications in the expression of non-phosphorylated MEK-1, ERK2 and GSK-3alpha/beta, as revealed by immunohistochemistry, were seen in AGD, but sarkosyl-insoluble fractions were particularly enriched in JNK-1 and alphaCaM kinase II. Increased expression of the phosphorylated (P) forms of MAPK/ERK, SAPK/JNK, p38 and GSK-3beta was found in grains and tau-containing cells in AGD. MAPK/ERK-P immunoreactivity was observed in pre-tangles and, diffusely, in the cytoplasm of ballooned neurons, but not in grains. Strong SAPK/JNK-P and P38-P, and moderate GSK-3b-P immunoreactivities selectively occured in grains, in neurons with pre-tangles and in the peripheral region of the cytoplasm of ballooned neurons. MAPK/ERK-P, SAPK/JNK-P, p38-P and GSK-3beta-P were expressed in tau-containing astrocytes and in oligodendrocytes with coiled bodies. Western blots revealed kinase expression in sarkosyl-insoluble fractions but none of the phospho-kinase antibodies recognized hyper-phosphorylated tau protein. These findings indicate complex, specific profiles of tau phosphorylation and concomitant activation of precise kinases that have the capacity to phosphorylate tau at specific sites in AGD. These kinases co-localize abnormal tau in selected structures and cells, including neurons with pre-tangles, ballooned neurons, astrocytes and oligodendrocytes. Most of these kinases are involved in cell death and cell survival in certain experimental paradigms. However, double-labeling studies with the method of in situ end-labeling of nuclear DNA fragmentation and cleaved (active) caspase-3 immunohistochemistry show no expression of apoptosis and death markers in cells bearing phosphorylated kinases.

Caspase-cleaved amyloid precursor protein in Alzheimer's disease

Caspase-3 mediated cleavage of the amyloid precursor protein (APP) has been proposed as a putative mechanism underlying amyloidosis and neuronal cell death in Alzheimer's disease (AD). We utilized an antibody that selectively recognizes the neo epitope generated by caspase-3 mediated cleavage of APP (alphadeltaC(csp)-APP) to determine if this proteolytic event occurs in senile plaques in the inferior frontal gyrus and superior temporal gyrus of autopsied AD and age-matched control brains. Consistent with a role for caspase-3 activation in AD pathology, alphadeltaC(csp)-APP immunoreactivity colocalized with a subset of TUNEL-positive pyramidal neurons in AD brains. AlphadeltaC(csp)-APP immunoreactivity was found in neurons and glial cells, as well as in small- and medium-size particulate elements, resembling dystrophic terminals and condensed nuclei, respectively, in AD and age-matched control brains. There were a larger number of alphadeltaC(csp)-APP immunoreactive elements in the inferior frontal gyrus and superior temporal gyrus of subjects with AD pathology than age-matched controls. AlphadeltaC(csp)-APP immunoreactivity in small and medium size particulate elements were the main component colocalized with 30% of senile plaques in the inferior frontal gyrus and superior temporal gyrus of AD brains. In some control brains, alphadeltaC(csp)-APP immunoreactivity appeared to be associated with a clinical history of metabolic encephalopathy. Our results suggest that apoptosis contributes to cell death resulting from amyloidosis and plaque deposition in AD.

Cell-cycle reentry and cell death in transgenic mice expressing nonmutant human tau isoforms

Mutations in the microtubule-associated protein tau gene have been linked to neurofibrillary tangle (NFT) formation in several neurodegenerative diseases known as tauopathies; however, no tau mutations occur in Alzheimer's disease, although this disease is also characterized by NFT formation and cell death. Importantly, the mechanism of tau-mediated neuronal death remains elusive. Aged mice expressing nonmutant human tau in the absence of mouse tau (htau mice) developed NFTs and extensive cell death. The mechanism of neuron death was investigated in htau mice, and surprisingly, the presence of tau filaments did not correlate directly with death within individual cells, suggesting that cell death can occur independently of NFT formation. Our observations show that the mechanism of neurodegeneration involved reexpression of cell-cycle proteins and DNA synthesis, indicating that nonmutant tau pathology and neurodegeneration may be linked via abnormal, incomplete cell-cycle reentry.

No difference in expression of apoptosis-related proteins and apoptotic morphology in control, pathologically aged and Alzheimer's disease cases

Apoptotic-like changes in the neocortex of control, pathologically aged and Alzheimer's disease (AD) cases were investigated. There was no increase in labeling or change in localization of labeling that distinguished between these cases for active caspase-3, -8, -9, Bax, Bcl-2 or TRADD. Bax, Bcl-2 and TRADD mRNA levels also differed little between case types, although there were small but significant decreases in Bax mRNA levels in AD compared to control cases and Bcl-2 mRNA in AD cases compared to pathologically aged and control cases. There was no difference in the percentage of apoptotic-like nuclei between these cases, except for a small but significant decrease in the inferior temporal gyrus of AD cases relative to controls. Nuclei observed within or adjacent to beta-amyloid plaques were rarely abnormal, and neurons bearing neurofibrillary tangles (NFTs) did not have abnormal nuclei. Apoptosis may not play a major role in the pathogenesis of neuronal degeneration of AD.

Early melatonin supplementation alleviates oxidative stress in a transgenic mouse model of Alzheimer's disease

Multiple lines of evidence demonstrated that increased brain oxidative stress is a key feature of Alzheimer's disease (AD). Melatonin is a potent endogenous antioxidant and free radical scavenger. A transgenic mouse model for AD mimics the accumulation of senile plaques, neuronal loss, and memory impairment. Four-month-old transgenic mice were administrated melatonin at 10 mg/kg for 4 months. We investigated the long-term influence of melatonin on these mice before amyloid plaques were deposited. We found an increase in the levels of brain thiobarbituric acid-reactive substances (TBARS) and a decrease in glutathione (GSH) content, as well as accelerated upregulation of the apoptotic-related factors, such as Bax, caspase-3, and prostate apoptosis response-4 (Par-4) in transgenic mice, but not in wild-type (WT) littermates. Significantly, the increase in TBARS levels, reduction in superoxide dismutase activity, and GSH content were reinstated by melatonin. In addition, transgenic mice administered melatonin (10 mg/kg) showed a significant reduction in upregulated expression of Bax, caspase-3 and Par-4, indicating inhibited triggering of neuronal apoptosis. These results supported the hypothesis that oxidative stress was an early event in AD pathogenesis and that antioxidant therapy may be beneficial only if given at this stage of the disease process. In sharp contrast to conventional antioxidants, melatonin crosses the blood-brain barrier, is relatively devoid of toxicity, and constitutes a potential therapeutic candidate in AD treatment.

Skin sensitivity to UVB irradiation in systemic lupus erythematosus is not related to the level of apoptosis induction in keratinocytes

OBJECTIVES

Accumulation of apoptotic cells has been suggested to be involved in the pathogenesis of systemic lupus erythematosus (SLE). As sunlight exposure is one of the factors that can trigger disease activity, we hypothesized that UV light may induce increased numbers of apoptotic cells in SLE.

METHODS

Fourteen SLE patients and 16 controls were irradiated with UVB to determine their minimal erythemal dose (MED). Subsequently, skin was irradiated with 1 MED and 2 MED, respectively, and after 24 h skin biopsies were analysed immunohistologically for the number of apoptotic cells and presence of pyknotic nuclear debris.

RESULTS

MED was significantly decreased in SLE patients and the presence of decreased MED was associated with a history of butterfly rash. Decreased MED was not related to other skin-related ACR criteria or to autoantibody specificities. No differences were detected in the numbers of apoptotic keratinocytes between patients and controls or in the amount of pyknotic nuclear debris following 1 and 2 MED irradiation, respectively. Absolute UVB doses were correlated with the number of apoptotic keratinocytes; dose-responses did not differ significantly between patients and controls.

CONCLUSIONS

Increased sensitivity of SLE patients to UVB, although associated with a history of malar rash, is not related to increased induction of apoptosis or increased levels of secondary necrosis in the skin. Thus, compared with controls, UVB-induced apoptosis is not increased in SLE patients under physiological conditions.

Grey Matter Pathology in Multiple Sclerosis

The aim of our study is to evaluate the extent and distribution of grey matter demyelinating lesions in multiple sclerosis (MS), addressing also neuronal loss and synaptic loss. Whole coronal sections of 6 MS brains and 6 control brains were selected. Immunohistochemistry was performed for myelin basic protein, neurofilaments, synaptophysin, ubiquitin, and activated caspase-3. Neuronal density and optical density of synaptophysin staining were estimated in cortical lesions and compared with those observed in corresponding areas of normal (i.e. nondemyelinated) cortex in the same section. Demyelinating lesions were observed in the cerebral cortex, in the thalamus, basal ganglia, and in the hippocampus. The percentage of demyelinated cortex was remarkable in 2 cases of secondary progressive MS (48% and 25.5%, respectively). Neuronal density was significantly reduced in cortical lesions (18-23% reduction), if compared with adjacent normal cortex, in the 2 cases showing the higher extent of cortical demyelination; in the same cases, very rare apoptotic neurons expressing caspase-3 were observed in cortical lesions and not in adjacent normal cortex. No significant decrease in optical density of synaptophysin staining was observed in cortical lesions. Grey matter demyelination and neuronal loss could contribute to disability and cognitive dysfunctions in MS.

The ubiquitin–proteasome system in Creutzfeldt–Jakob and Alzheimer disease: Intracellular redistribution of components correlates with neuronal vulnerability

Creutzfeldt-Jakob (CJD) and Alzheimer disease (AD) are accompanied by selective neuronal loss in the brain. We examined the regional and subcellular immunolocalization of ubiquitin, proteasomal subunits, and the heat-shock protein Hsp72 in control, CJD, and AD cases. In control and non-affected areas of disease cases, 20S proteasomes, 19S regulatory subunits, S6a, S6b, and S10b exhibit mainly cytoplasmic, whereas S4 and S7 show predominantly nuclear localization. The intensity of immunostaining for ubiquitin, proteasomal subunits, and Hsp72 varies in different anatomical regions both in disease and control brains. Areas with weaker immunolabeling correspond to affected areas in CJD and AD. In disease cases, antibodies for 20S, S4, S6b, S7, and ubiquitin intensely immunolabel neuronal nuclei of vulnerable cells in affected areas. Our results suggest that the ubiquitin-proteasome system takes part in the pathogenesis of neurodegeneration. Ubiquitin, Hsp72, and proteasomal ATPases possibly play a role in protecting certain neuronal populations in CJD and AD.

Human adult olfactory neuroepithelial derived progenitors retain telomerase activity and lack apoptotic activity

Olfactory epithelium (OE) contains a population of progenitors responsible for its life-long regenerative capacity. Procedures for the isolation of these progenitors have been established [F.J. Roisen, K.M. Klueber, C.L. Lu, L.M. Hatcher, A. Dozier, C.B. Shields, Adult human olfactory stem cells, Brain Res., 890 (2001) 11-12.] and over 40 patient-specific cell lines from adult postmortem OE and endoscopic biopsy from patients undergoing nasal sinus surgery have been obtained. As these cells emerged in primary cultures, they formed neurospheres (NSFCs). The purpose of the present study was to further characterize these adult human olfactory-derived progenitors. Subcultures of the NSFCs have been passaged nearly 200 times, with a mitotic cycle of 18-20 h. Telomerase activity remains in stem cells; therefore, ELISA was employed to determine the telomerase activity of different lines and passages. Since progenitors undergo low levels of apoptosis, the levels of apoptosis were also examined in these populations. The levels of telomerase and apoptotic activity in 12 NSFC lines remained relatively constant irrespective of donor age, culture duration, or sex. To further study the apoptotic characteristics of the NSFCs, nine different caspases (cysteine proteases) known to be critical in apoptosis were evaluated using gene-microarrays comparing cells from a single line at passages 14, 88, and 183. No increases were found in caspase activity in all passages studied. ELISA confirmed the absence of caspase activity over the entire range of passages. This study further suggests that NSFCs can be obtained and used from patients, irrespective of age, sex, or time in culture without altered viability expanding the potential utility of these cells for autologous transplantation and possible diagnostic testing.

Heat shock treatment protects osmotic stress-induced dysfunction of the blood-brain barrier through preservation of tight junction proteins

The blood-brain barrier (BBB) is a specialized structure in the central nervous system (CNS), which participates in maintenance of a state of cerebrospinal fluid homeostasis. The endothelial cells of the cerebral capillaries and the tight junctions between them form the basis of the BBB. Research has shown that destruction of the BBB is associated with diseases of the CNS. However, there is little research on how the BBB might be protected. In this study, we used a high osmotic solution (1.6 M D-mannitol) to open the BBB of rats and Evans blue dye as a macromolecular marker. The effect of heat shock treatment was evaluated. The results show that increased synthesis of heat shock protein 72 (Hsp72) was induced in the heated group only. BBB permeability was significantly less in the heat shock-treated group after hyperosmotic shock. The major tight junction proteins, occludin and zonula occludens (ZO)-1, were significantly decreased after D-mannitol treatment in the nonheated group, whereas they were preserved in the heated group. The coimmunoprecipitation studies demonstrated that Hsp72 could be detected in the precipitates of brain extract interacting with anti-ZO-1 antibodies as well as those interacting with anti-occludin antibodies in the heated group. We conclude that the integrity of tight junctions could be maintained by previous heat shock treatment, which might be associated with the increased production of Hsp72.

Tissue preconditioning may explain concentric lesions in Baló's type of multiple sclerosis

Lesions of Baló's concentric sclerosis are characterized by alternating layers of myelinated and demyelinated tissue. The reason for concentric demyelination in this variant of multiple sclerosis is unclear. In the present study we investigated the immunopathology in autopsy tissue of 14 patients with acute multiple sclerosis or fulminant exacerbations of chronic multiple sclerosis with Baló-type lesions in the CNS, focusing on the patterns of tissue injury in actively demyelinating lesions. We found that all active concentric lesions followed a pattern of demyelination that bears resemblances to hypoxia-like tissue injury. This was associated with high expression of inducible nitric oxide synthase in macrophages and microglia. At the edge of active lesions and, less consistently, in the outermost layer of preserved myelin, proteins involved in tissue preconditioning, such as hypoxia-inducible factor 1alpha and heat-shock protein 70, were expressed mainly in oligodendrocytes and to a lesser degree also in astrocytes and macrophages. Due to their neuroprotective effects, the rim of periplaque tissue, where these proteins are expressed, may be resistant to further damage in an expanding lesion and may therefore remain as a layer of preserved myelinated tissue.

Ischemia leads to apoptosis--and necrosis-like neuron death in the ischemic rat hippocampus

Morphological evidence of apoptosis in transient forebrain ischemia is controversial. We therefore investigated the time sequence of apoptosis-related antigens by immunohistochemistry and correlated it with emerging nuclear patterns of cell death in a model of transient forebrain ischemia in CA1 pyramidal cells of the rat hippocampus. The earliest ischemic changes were found on day 2 and 3, reflected by an upregulation of phospho-c-Jun in a proportion of morphologically intact CA1 neurons, which matched the number of neurons that succumbed to ischemia at later time points. At day 3 and later 3 ischemic cell death morphologies became apparent: pyknosis, apoptosis-like cell death and necrosis-like cell death, which were confirmed by electron microscopy. Activated caspase-3 was present in the vast majority of cells with apoptosis-like morphology as well as in a small subset of cells undergoing necrosis; its expression peaked on days 3 to 4. Silver staining for nucleoli, which are a substrate for caspase-3, revealed a profound loss of nucleoli in cells with apoptosis-like morphology, whereas cells with necrosis-like morphology showed intact nucleoli. Overall, cells with apoptosis-like morphology and/or caspase-3 expression represented a minor fraction (<10%) of ischemic neurons, while the vast majority followed a necrosis-like pathway. Our studies suggest that CA1 pyramidal cell death following transient forebrain ischemia may be initiated through c-Jun N-terminal kinase (JNK) pathway activation, which then either follows an apoptosis-like cell death pathway or leads to secondary necrosis.

Brain aging phenomena in migrating sockeye salmon Oncorhynchus nerka nerka

Aging, a process occurring in all vertebrates, is closely related to a loss in physical and functional abilities. There is widespread interest in clarifying the relevance of environmental, metabolic, and genetic factors for vertebrate aging. In the Pacific salmon a dramatic example of aging is known. Looking for changes in the salmon brain, perhaps even in the role of initiating the aging processes, we investigated several biochemical parameters that should reflect brain functional activity and stress response such as the neurotransmitters dopamine, and serotonin, and two of their respective metabolites 3,4-dihydroxyphenylacetic acid, and 5-hydroxyindole acetic acid, as well as glutathione, glutathione disulfide, and the extent of terminal deoxynucleotidyltransferase-mediated dUTP nick end-labelling. The aging of migrating sockeye salmon (Oncorhynchus nerka nerka) is accompanied by gradual increase in dopamine and serotonin turnover and a gradual decrease of brain total protein and glutathione levels. There appears to be an increased need for detoxification of reactive biological intermediates since activities of superoxide dismutase and catalase increase with age. However, our data do not support a major increase in apoptotic cell death during late aging but rather implicate an age related downward regulation of protein and glutathione synthesis and proteolysis increasing the need for autophagocytosis or heterophagocytosis in the course of cell death.

Zinc-induced anti-apoptotic effects in SH-SY5Y neuroblastoma cells via the extracellular signal-regulated kinase 1/2

Zinc levels are increased in brain areas severely affected by Alzheimer's disease (AD) pathologies. Zinc has both protective and neurotoxic properties and can stimulate both phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways. Several kinases related to these pathways including protein kinase B (PKB), p70 S6 kinase (p70S6K), and extracellular signal-regulated kinase 1/2 (ERK1/2) are known cell survival factors and are overactivated in neurons bearing neurofibrillary tangles (NFTs) in AD. The present study aimed to determine whether anti-apoptotic effects of zinc are mediated via these signaling pathways. Zinc was used to treat SH-SY5Y neuroblastoma cells and effects investigated in relation to PKB, p70S6K, and ERK1/2 in the absence and presence of the pro-apoptotic agent staurosporine (STS). Cell damage was evaluated by measuring levels of DNA fragmentation as well as the WST-1 assay for cell viability. Results indicated that: (1) treatment with high doses of zinc (>/=400 microM) for short time periods (</=2 h) gave rise to increased levels of DNA fragments, increased cell membrane permeability, and reduced mitochondria membrane potential; (2) treatment with 100 microM zinc for >2 h reversed an increased DNA fragmentation due to U0126 inhibition of ERK1/2; (3) increased DNA fragmentation due to STS could be protected against by 100 microM zinc; (4) the protective effects of 100 microM zinc on STS-induced DNA fragmentation could be partially reversed by U0126. These results indicate that a zinc-induced anti-apoptotic response in SH-SY5Y cells likely occurs through ERK1/2.

Flow cytometry as a method for studying effects of stressors on primary rat neurons

The mechanisms associated with cell death have been an important focus for neurobiology research. In the present study, the methodology of flow cytometry was used to optimize quantification of the toxic effects of tumor necrosis factor-alpha (TNF-alpha), trans-4-hydroxy-2-nonenal (4-HNE), and aged amyloid-beta (Abeta1-42) on rat primary cortical neurons. The fluorescent dyes annexin V-FITC and propidium iodide (PI) were used to identify populations of viable, early apoptotic, necrotic and late apoptotic cells by flow cytometry. Prior to exposure, the primary cultures showed 83% cell viability. Flow cytometry following labeling of cells with a specific neuronal marker, TUJ-1, revealed 82% pure neuronal populations, whereas approximately 7% were astrocytic as shown by glial fibrillary acidic protein positivity. Exposure of primary cultures to TNF-alpha, 4-HNE, and aged Abeta1-42 gave an increased number of early apoptotic cells. We show that flow cytometry is a suitable method for quantifying effects of different stressors on neurons in primary cultures. This technique could be useful for screening and testing of pharmacological compounds relevant to neurodegenerative disorders.

Can lenticular factors improve the posttrauma fate of neurons?

The intraocular lens has recently been recognized as a potential source for neuroprotective and neurite-promoting activities. The lens is ontogenetically and functionally a peculiar intraocular tissue with the unique feature of performing incomplete cellular apoptosis throughout the lifetime. The ectodermally derived epithelial cells permanently divide to produce the nuclei- and organelle-free lens fibre cells that allow for the optical transparency. The underlying extremely specific physical, biochemical, metabolic and structural mechanism lead to efficient protection from photo-oxidative stress caused by exposure to short-wavelength light. The fact that fibre cells undergo incomplete apoptosis is also of crucial importance to other cellular systems. In particular, injured nerve cells such as axotomized retinal ganglion cells may profit from the apoptosis-blocking mechanisms operating within the lens fibres. In this review we first discuss some factors involved in the lens differentiation and partial apoptosis as a basic principle of long-term survival. We then present recent experimental evidence that lenticular factors also operate outside the lens, and in particular within the retina to contribute to axonal regeneration, e.g. after a trauma. In turn, factors such as GAP-43 that were thought to be exclusively expressed within nervous tissue have now also been discovered within the lenticular tissue. Experiments of the direct confrontation of lenticular epithelial and fibre cells with regenerating ganglion cell axons in vitro are presented. It is concluded that survival factors supplied by the lens might be used to facilitate survival within neuronal tissue.

CA1 hippocampal neuronal loss in familial Alzheimer's disease presenilin-1 E280A mutation is related to epilepsy

PURPOSE

Alzheimer disease (AD) and epilepsy are brain disorders frequently associated with neuronal cell loss in mesial temporal lobe structures, but presenting different patterns of damage. Recently it was proposed that a causal relation may exist between AD pathology and the appearance of epilepsy in some cases with AD. This study aimed to determine the neuronal loss in CA1 hippocampal region from patients bearing the presenilin-1 [E280A] mutation (PS1[E280A]) associated with seizures.

METHODS

Coronal sections from the hippocampal formation (anterior one third) from controls (n = 5) and familial AD (FAD; n = 8) patients were stained by using thionin and thioflavine-S staining to evaluate the number of neurons in the CA1 field, beta-plaques, and neurofibrillary tangles, respectively.

RESULTS

Two distinct patterns of neuronal loss in the CA1 field of FAD patients were found: (a) diffuse-patchy neuronal loss (three FAD nonepilepsy patients) characterized by both a general decrease of neurons and the presence of multiple, small regions devoid of neurons; and (b) sclerotic-like neuronal loss (five FAD epilepsy patients) similar to that found typically in the CA1 field of epilepsy patients with hippocampal sclerosis.

CONCLUSIONS

This investigation shows for the first time CA1 neuronal depopulation in a subpopulation of patients (five of eight) bearing the PS1[E280A] mutation with epileptic seizures, indicating a relation between hippocampal neuronal loss and epileptic seizures in FAD patients.

Apoptotic mechanisms in Alzheimer neurofibrillary degeneration: cause or effect?

Increasing evidence suggests that selective neuronal loss in neurodegenerative diseases involves activation of cysteine aspartyl proteases (caspases), which initiate and execute apoptosis. In Alzheimer disease both extracellular amyloid deposits and intracellular amyloid beta protein may activate caspases, leading to cleavage of nuclear and cytoskeletal proteins, including tau protein. Proteolysis of tau may be critical to neurofibrillary degeneration, which correlates with dementia.

Apoptosis in oligodendrocytes is associated with axonal degeneration in P301L tau mice

Transgenic mice overexpressing human tau with the P301L mutation develop neurofibrillary tangles, extensive gliosis, adult-onset motor abnormalities, and neuronal loss in affected brain regions. We investigated the mechanism of neuronal cell death in this model of tauopathy. There was no evidence of neuronal apoptosis at any age; however, a population of oligodendorocytes was immunopositive for TUNEL and activated caspase-3. EM confirmed that these oligodendrocytes were undergoing apoptosis. These data suggest that classical apoptosis is not a major mechanism of neuronal cell death associated with the tau dysfunction in this mouse model; however, prominent white matter pathology in the spinal cord suggests that axonal degeneration in dying neurons causes oligodendrocytes to undergo apoptosis. It is unknown if loss of oligodendrocytes either through apoptosis or through the formation of intracellular tau lesions further contributes to the neurodegeneration seen in these mice.

The facial nerve axotomy model

Experimental models such as the facial nerve axotomy paradigm in rodents allow the systematic and detailed study of the response of neurones and their microenvironment to various types of challenges. Well-studied experimental examples include peripheral nerve trauma, the retrograde axonal transport of neurotoxins and locally enhanced inflammation following the induction of experimental autoimmune encephalomyelitis in combination with axotomy. These studies have led to novel insights into the regeneration programme of the motoneurone, the role of microglia and astrocytes in synaptic plasticity and the biology of glial cells. Importantly, many of the findings obtained have proven to be valid in other functional systems and even across species barriers. In particular, microglial expression of major histocompatibility complex molecules has been found to occur in response to various types of neuronal damage and is now regarded as a characteristic component of "glial inflammation". It is found in the context of numerous neurodegenerative disorders including Parkinson's and Alzheimer's disease. The detachment of afferent axonal endings from the surface membrane of regenerating motoneurones and their subsequent displacement by microglia ("synaptic stripping") and long-lasting insulation by astrocytes have also been confirmed in humans. The medical implications of these findings are significant. Also, the facial nerve system of rats and mice has become the best studied and most widely used test system for the evaluation of neurotrophic factors.

Complement activation in human prion disease

The central event in the neuropathological process of prion diseases (PrD) is the accumulation of abnormal prion protein accompanied by severe neuronal loss. Despite the infectious nature of these diseases, no prominent immune response has been detected yet. However, recent studies have shown that complement, a component of the innate immune system, is involved in the early pathogenesis of experimental prion infection. Here we demonstrate, in the diseased human brains, the presence of active compounds of the complement system, like C1q and C3b, in extracellular disease-associated prion protein deposits and the membrane attack complex in neurons. The neuronal localization of the membrane attack complex correlates well with the severity of disease-specific pathology and TUNEL labeling of neurons, irrespective of genotype or molecular phenotype of human prion diseases.

Expression of nestin in Purkinje cells in patients with Creutzfeldt-Jakob disease

Nestin is one of the intermediate filament proteins and mainly expressed during the development of the central nervous system. We examined the cerebellum of patients with Creutzfeldt-Jakob disease (CJD), multiple system atrophy and amyotrophic lateral sclerosis, using anti-human nestin antibodies. The antibodies strongly immunostained the cytoplasm, dendrites and torpedoes of Purkinje cells in CJD. However, Purkinje cells in other neurodegenerative disorders were not nestin-immunoreactive. Nestin immunoreactivities became more marked as the pathological severity in the cerebellum increased. Our findings suggest that nestin is strongly expressed in Purkinje cells in pathologically advanced CJD and show the possibility that Purkinje cells are being reactivated to promote survival.

A three amino acid peptide, Gly-Pro-Arg, protects and rescues cell death induced by amyloid β-peptide

Amyloid beta-peptide (Abeta) contributes to the pathogenesis of Alzheimer's disease (AD), causing neuronal death through apoptosis. In this study, the neuroprotective role of small peptides, Gly-Pro-Glu (GPE), Gly-Glu (GE), Gly-Pro-Asp (GPD), and Gly-Pro-Arg (GPR) were examined against Abeta-induced toxicity in cultured rat hippocampal neurons. We report here that GPR (10-100 microM) prevented Abeta-mediated increase in lactate dehydrogenase (LDH) release and Abeta inhibition of MTT reduction, even in neurons that were pre-exposed to Abeta for 24 or 48 h. Since GPR prevented Abeta inhibition of MTT reduction, the anti-apoptotic effect of GPR was studied by examining activation of caspase-3 and expression of p53 protein. Caspase-3 was significantly activated by 20 microM Abeta25-35 and 5 microM Abeta1-40, but GPR effectively prevented the Abeta-mediated activation of caspase-3. Similarly, Abeta increased numbers of p53-positive cells, but GPR prevented this Abeta effect. Our findings suggest that GPR can rescue cultured rat hippocampal neurons from Abeta-induced neuronal death by inhibiting caspase-3/p53-dependent apoptosis.

Is DNA repair compromised in Alzheimer's disease?

Mammalian cells utilize multiple mechanisms to repair DNA damage that occurs during normal cellular respiration and in response to genotoxic stress. This study sought to determine if chronic oxidative stress proposed to occur during Alzheimer's disease alters the expression or activity of DNA double-strand break repair or base excision repair proteins. Double-strand break repair requires DNA-dependent protein kinase, composed of a catalytic subunit, DNA-PKcs, and a regulatory component, Ku. Ku DNA binding activity was reduced in extracts of postmortem AD midfrontal cortex, but was not significantly different from the age-matched controls. Decreased Ku DNA binding correlated with reduced protein levels of Ku subunits, DNA-PKcs, and poly(ADP-ribose) polymerase-1. Expression of the base excision repair enzyme Ref-1, however, was significantly increased in AD extracts compared to controls. Ku DNA binding and DNA-PK protein levels in the AD cases correlated significantly with synaptophysin immunoreactivity, which is a measure of synaptic loss, a major correlate of cognitive deficits in AD. Immunohistochemical analysis suggested that DNA-PK protein levels reflected both number of neurons and regulation of cellular expression.

Neurofibrillary degeneration of the Alzheimer-type: an alternate pathway to neuronal apoptosis?

Neuronal death is a process which may be either physiological or pathological. Apoptosis and necrosis are two of these processes which are particularly studied. However, in neurodegenerative disorders, some neurons escape to these types of death and "agonize" in a process referred to as neurofibrillary degeneration. Neurofibrillary degeneration is characterized by the intraneuronal aggregation of abnormally phosphorylated microtubule-associated Tau proteins. A number of studies have reported a reactivation of the cell cycle in the neurofibrillary degeneration process. This reactivation of the cell cycle is reminiscent of the initiation of apoptosis in post-mitotic cells where G1/S markers including cyclin D1 and cdk4/6, are commonly found. However, in neurons exhibiting neurofibrillary degeneration, both G1/S and G2/M markers are found suggesting that they do not follow the classical apoptosis and an aberrant cell cycle occurs. This aberrant response leading to neurofibrillary degeneration may be triggered by the sequential combination of three partners: the complex Cdk5/p25 induces both apoptosis and the "abnormal mitotic Tau phosphorylation". These mitotic epitopes may allow for the nuclear depletion of Pin1. This latter may be responsible for escaping classical apoptosis in a subset of neurons. Since neurofibrillary degeneration is likely to be a third way to die, molecular mechanisms leading to changes in Tau phosphorylation including activation of kinases such as cdk5 or other regulators such as Pin1 could be important drug targets as they are possibly involved in early stages of neurodegeneration.

Quantitative assessment of DNA fragmentation and beta-amyloid deposition in insular cortex and midfrontal gyrus from patients with Alzheimer's disease

It has been suggested that the neurodegeneration that occurs with Alzheimer's disease (AD) may result from apoptosis, a process of programmed cell death. Neuronal injury, induced by abnormal aggregates of beta-amyloid peptide, has been identified as an apoptotic trigger. In the present study, brain tissue samples were obtained from the insular cortex (INS) and midfrontal gyrus (MFG) of Alzheimer subjects and age-matched, nondemented controls. Tissue sections from all samples were alternately stained by an in situ TUNEL assay to identify 3' termini DNA strand breaks characteristic of apoptosis or immunohistochemically for beta-amyloid deposition in senile plaques. The incidence of DNA fragmentation detected in pyramidal neurons was relatively infrequent overall, but was significantly higher in AD compared to controls. AD subjects consistently exhibited a dense accumulation of plaques, with a twofold greater concentration in MFG as INS. There was no significant difference in pyramidal cell number regardless of subject or brain region. Taken together, our results indicate that the TUNEL assay may be revealing cell damage rather than cell loss. Our finding of a moderate correlation between the incidence of TUNEL-positive cells and plaque density implicates beta-amyloid as one of multiple factors provoking cell injury in AD. A notable contribution of this study is the identification of distinctive neuropathologies co-occurring in two brain regions interconnected with each other and with limbic and cortical areas typically damaged during AD.

Is the cell death in mesial temporal sclerosis apoptotic?

PURPOSE

Mesial temporal sclerosis (MTS) is characterized by neuronal loss in the hippocampus. Studies on experimental models and patients with intractable epilepsy suggest that apoptosis may be involved in neuronal death induced by recurrent seizures.

METHODS

We searched evidence for apoptotic cell death in temporal lobes resected from drug-resistant epilepsy patients with MTS by using the terminal deoxynucleotidyl transferase (TdT) and digoxigenin-11-dUTP (TUNEL) method and immunohistochemistry for Bcl-2, Bax, and caspase-cleaved actin fragment, fractin. The temporal lobe specimens were obtained from 15 patients (six women and nine men; mean age, 29 +/- 8 years).

RESULTS

Unlike that in normal adult brain, we observed Bcl-2 immunoreactivity in some of the remaining neurons dispersed throughout the hippocampus proper as well as in most of the reactive astroglia. Bax immunopositivity was increased in almost all neurons. Fractin immunostaining, an indicator of caspase activity, was detected in approximately 10% of these neurons. Despite increased Bax expression and activation of caspases, we could not find evidence for DNA fragmentation by TUNEL staining. We also could not detect typical apoptotic changes in nuclear morphology by Hoechst-33258 or hematoxylin counterstaining.

CONCLUSIONS

These data suggest that either apoptosis is not involved in cell loss in MTS, or a very slow rate of cell demise may have precluded detecting TUNEL-positive neurons dying through apoptosis. Increased Bax expression and activation of caspases support the latter possibility.

Apoptosis: programmed cell death at a molecular level

OBJECTIVES

To characterize cell surface receptors, their ligands, and their proteins in the 2 major pathways of apoptosis; the components that promote/suppress these interactions; the noninflammatory removal of apoptotic bodies by dendritic cells; and methods of assay in studies of cell death. To describe: how deregulation of apoptosis may contribute to autoimmunity, cancer, and neurodegenerative disorders and strategies some viruses have evolved that interfere with the host's apoptotic pathways.

METHODS

The authors reviewed and compiled literature on the extrinsic (tumor necrosis factor [TNF] receptor superfamily and ligands) and intrinsic (mitochondria-associated) apoptotic pathways, the pro- and antiapoptotic proteins of the B-cell follicular lymphoma (Bcl)-2 family, the nuclear factor (NF)-kappaB family of proteins, commonly used laboratory methods to distinguish apoptosis from necrosis, the recognition and removal by phagocytosis of apoptotic cells by dendritic cells, and viral strategies to avoid a host's apoptotic response.

RESULTS

The 2 major pathways of apoptosis are (1). FasL and other TNF superfamily ligands induce trimerization of cell-surface death receptors and (2). perturbated mitochondria release cytochrome c, the flavoprotein apoptosis-inducing factor, and second mitochondria-derived activator of caspases/DIABLO (a protein that directly neutralizes inhibitors of apoptotic proteins and activates proteases). Catalytically inactive cysteine proteases, called caspases, and other proteases are activated, ultimately leading to cell death with characteristic cellular chromatin condensation and DNA cleavage to fragments of approximately 180 bp. The inhibitory/promoting action of Bcl-2 family members is involved in the release of cytochrome c, an essential factor for the mitochondrial-associated pathway. A balance between inhibition/promotion determines a cell's fate. The NF-kappaB family in the cytoplasm of cells activates various genes carrying the NF-kappaB response element, such as members of the inhibitor of apoptotic proteins family. A few of the more common methods to detect apoptotic cell death are described, which use immunochemical, morphologic and flow cytometric methods, and genetic markers. Exposed phosphatidylserine at the outer leaflet of the plasma membrane of the apoptotic cell serves as a possible receptor for phagocytosis by immature dendritic cells. These cells phagocytize both apoptotic and necrotic cells, but only the latter induce maturation to become fully functional antigen-presenting cells. Viral inhibitors of apoptosis allow increased virus replication in cells, possibly resulting in their oncogenicity.

CONCLUSIONS

Balanced apoptosis is crucial in development and homeostasis, and all multicellular organisms have a physiologically programmed continuum of pathways to apoptotic cell death. Further studies of the control at the molecular level of key components and promoters/suppressors of apoptosis may provide better approaches to treatment of autoimmune diseases, malignancies, and neurodegenerative disorders. Many important questions remain regarding the advantages of modifying apoptotic programs in clinical situations.

Association of phosphorylation site of tau protein with neuronal apoptosis in Alzheimer's disease

In addition to neuritic changes and amyloid deposits, neuronal and glial cell apoptosis is an important pathological feature of Alzheimer's disease (AD). Several factors have been postulated as causes or triggers of cellular apoptotic change. This study focused on a quantifiable relationship between phosphorylation sites of tau protein in the neurofibrillary tangles (NFT) and neuronal apoptosis. Five monoclonal anti-tau antibodies (AT180, AT8, HT7, Tau2 and Tau5) for NFT labeling and TdT-mediated UTP nick-end labeling (TUNEL) for localizing apoptotic change were employed. TUNEL-stained neuronal nuclei showed significantly high density in the entorhinal cortex, cornu ammonis (CA) and the parietal cortex. In all regions, density of TUNEL-stained neuronal nuclei showed significantly direct correlation with that of AT8-, AT180- and Tau2-positive neurons. Correlation of TUNEL-stained neuronal nuclei with tau-positive neurons differed depending on the cerebral regions. Density of TUNEL-stained neuronal nuclei showed inverse correlation with that of both AT8-positive and Gallyas-stained NFT in the CA and showed significantly direct correlation with AT8- and HT7-positive neurons in the frontal cortex. Density of tau-positive and Gallyas-stained NFT was higher than that of TUNEL-stained nuclei. We conclude that phosphorylation sites of tau, 159-163 and 202-205, are probably associated with neuronal apoptosis and apoptotic change follows abnormal phosphorylation of tau.

Apoptotic promoters and inhibitors in Alzheimer's disease: Who wins out?

A spectrum of apoptotic mediators are seen in neurons that are vulnerable in Alzheimer's disease (AD), leading many investigators to suggest that neuronal death in AD is mediated by an apoptotic process. Indeed, the environment of the AD brain is awash with proapoptotic mediators including amyloid-beta, oxidative stress, hydroxynonenal oxidants and metabolic alterations with concomitant energy failures. However, the phenotype that defines the terminal events that are pathogonomic of apoptosis, such as chromatin condensation, apoptotic bodies and membrane blebbing, are not seen in AD. Therefore, we speculated that, although AD presents with a proapoptotic environment, apoptosis does not proceed to completion. In this regard, we found that while the initiator phases of apoptosis were engaged, this does not lead to the activation of the terminal commitment phase necessary for apoptotic cell death. In other words, in AD, there is a lack of effective apoptotic signal propagation to distal effectors. This is a novel phenomenon (which we term abortosis) that represents an inhibition of apoptosis at the postinitiator stage in neurons that survive in AD.

Nitric oxide synthase-3 overexpression causes apoptosis and impairs neuronal mitochondrial function: relevance to Alzheimer's-type neurodegeneration

Dementia in Alzheimer's disease (AD) is correlated with cell loss that is mediated by apoptosis, mitochondrial (Mt) dysfunction, and possibly necrosis. Previous studies demonstrated increased expression of the nitric oxide synthase 3 (NOS3) gene in degenerating neurons of AD brains. For investigating the role of NOS3 overexpression as a mediator of neuronal loss, human PNET2 central nervous system-derived neuronal cells were infected with recombinant adenovirus vectors that expressed either human NOS3 or green fluorescent protein cDNA under the control of a CMV promoter. NOS3 overexpression resulted in apoptosis accompanied by increased levels of p53, p21/Waf1, Bax, and CD95. In addition, NOS3 overexpression impaired neuronal Mt function as demonstrated by the reduced levels of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide and nicotinamide adenine dinucleotide (reduced form)-tetrazolium reductase activities and MitoTracker Red fluorescence. These adverse effects of NOS3 were associated with increased cellular levels of reactive oxygen species and impaired membrane integrity and were not produced in cells that were transfected with a cDNA encoding catalytically inactive NOS3. Importantly, modest elevations in NOS3 expression, achieved by infection with low multiplicities of adenovirus-NOS3 infection, did not cause apoptosis but rendered the cells more sensitive to oxidative injury by H(2)O(2) or diethyldithiocarbamate. In contrast, treatment with NO donors did not enhance neuronal sensitivity to oxidative injury. These results suggest that NOS3-induced neuronal death is mediated by Mt dysfunction, oxidative injury, and impaired membrane integrity, rather than by NO production, and that neuroprotection from these adverse effects of NOS3 may be achieved by modulating intracellular levels of oxidative stress.

Glycoxidative stress creates a vicious cycle of neurodegeneration in Alzheimer's disease--a target for neuroprotective treatment strategies?

Accumulation of Advanced Glycation Endproducts (AGEs) in the brain is a feature of ageing and degeneration, especially in Alzheimer's disease (AD). Increased AGE levels explain many of the neuropathological and biochemical features of AD such as extensive protein crosslinking (beta-amyloid and MAP-tau), glial activation, oxidative stress and neuronal cell death. Oxidative stress and AGEs initiate a positive feedback loop, where normal age-related changes develop into a pathophysiological cascade. Combined intervention using antioxidants, anti-inflammatory drugs and AGE-inhibitors may be a promising neuroprotective strategy.

Differential activation of caspase-3 at two maturational stages during okadaic acid-induced rat neuronal death

Okadaic acid (OA), a protein phosphatase inhibitor, is used as a research model of Alzheimer's disease to induce tau phosphorylation and neuronal death. We reported previously that OA induces neuronal apoptosis of immature neurons (in vitro days (IVD) 3-5), which is inhibited by cycloheximide (CHX). In this study, we demonstrate that CHX fails to prevent OA-induced neuronal death in mature neurons (IVD 14-15). Upon comparison of both types of dying cells, the immature neurons displayed characteristic features of apoptosis, such as nuclear fragmentation, phosphatidylserine externalization and prominent caspase-3 activation, while the mature neurons showed few characteristic features of apoptosis. Lack of the beneficial effects of CHX and the lesser activation of caspase-3 in the mature neurons argue against typical apoptotic neuronal death in the OA-induced neurodegeneration model.

Age-related progressive neuronal DNA damage associated with cerebral degeneration in a mouse model of accelerated senescence

The DNA of cerebral neurons in subjects with Alzheimer's disease is extensively damaged, although the morphological features of apoptosis are absent. We investigated whether DNA is damaged in the brains of the SAMP10 strain of mouse, in which accelerated senescence is characterized by age-related cerebral atrophy and cognitive impairment. We performed quantitative terminal deoxynucleotidyl transferase-mediated digoxigenin-labeled dUTP nick end labeling (TUNEL), using paraffin sections. TUNEL positive cells increased in number in the cerebral neurons of SAMP10 mice with aging. TUNEL positive cells were widely distributed in mice at age 13-14 months, and obvious in the olfactory tubercle, anterior cingulate cortex, insular cortex, and amygdala. These TUNEL positive cells did not have the morphological features of apoptosis. Therefore, the DNA became damaged with advancing age through a mechanism other than apoptosis. SAMP10 is a useful mouse model of brain aging that mimics the progressive neuronal DNA damage associated with human neurodegenerative disorders.

Fas (CD95/Apo-1)/Fas ligand expression in neonates with pontosubicular neuron necrosis

Pontosubicular neuron necrosis (PSN) represents an age-specific response to severe hypoxic-ischemic injury occurring in human neonates but not in older children or adults. Histologically, PSN is characterized by acute neuronal death in the pontine nuclei and the hippocampal subiculum bearing the hallmarks of apoptosis. In animal models of hypoxic-ischemic injury, induction of neuronal apoptosis can be triggered by Fas (CD95/Apo-1), a cell surface receptor of the tumor necrosis factor-alpha superfamily, which transduces apoptotic death signals when cross-linked by its natural ligand. Here, we have investigated the expression of Fas/Fas ligand in human autopsy material consisting of 13 PSN cases and 10 age-matched cases without PSN. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, immunohistochemistry, and double labeling for Fas/Fas ligand and the astrocyte marker glial fibrillary acid protein, the microglia/macrophage specific marker KiM1P, and the neuronal marker NeuN were performed on formalin-fixed brain specimens. Although mainly neurons of both PSN and controls expressed Fas receptor, expression was significantly increased (p = 0.001) in PSN cases in which predominantly degenerating cells with signs of early apoptosis showed Fas expression. In contrast, Fas ligand expression was found mainly on astrocytes and microglial cells. There was no significant difference between cases with and without PSN. We conclude that in the developing human brain, cells expressing the Fas receptor may be susceptible to undergoing apoptosis in response to hypoxic-ischemic injury.

Frequency and distribution of TUNEL-positive neurons in brains of dementia with Lewy bodies: comparison with those in brains of Alzheimer's disease

The present study investigated the frequency and distribution of TUNEL-positive neurons in brains of dementia with Lewy bodies (DLB) in comparison with those in brains of Alzheimer's disease (AD), Down syndrome (DS) and non-demented elderly persons. In DLB brains, TUNEL-positive neurons were increased in frequency compared with those in non-demented elderly brains, and showed a distribution similar to those in AD and DS brains. DLB cases with TUNEL-positive neurons showing severe Lewy pathology were all neocortical type, while DLB cases of the limbic type showing mild Lewy pathology did not demonstrate TUNEL-positive neurons. In addition, we investigated the relationships between TUNEL-positive neurons and pathological hallmarks of DLB or AD brains. TUNEL-positive neurons had no Lewy bodies or neurofibrillary tangles, and were not located within amyloid deposits. These findings suggest that neuronal damage showing DNA fragmentations occurs in DLB brains as well as in AD and DS brains, and that it is accelerated by progression of Lewy pathology as well as Alzheimer pathology, although it is not directly related to their pathological hallmarks.

Prominent stress response of Purkinje cells in Creutzfeldt-Jakob disease

To examine the role of stress-related 70-kDa heat shock proteins (Hsp-s) in Creutzfeldt-Jakob disease (CJD), we performed immunocytochemistry to detect Hsp-72 and Hsp-73, together with the abnormal (PrP(Sc)) and the presumed cellular form (PrP(C)) of the prion protein, and TUNEL method to measure cellular vulnerability in different brain regions in CJD and control cases. While Hsp-73 showed uniform distribution in all the examined samples, an increase in the number of Purkinje cells with prominent accumulation of Hsp-72 in the CJD group was observed. These neurons also showed intense PrP(C) staining, but TUNEL-positive nuclei were only detected in the granular (Hsp-72-negative) cell layer. Fewer cells of the inferior olivary nucleus were immunoreactive for Hsp-72 in CJD than in control cases, and regions showing severe spongiform change and gliosis exhibited fewer Hsp-72-immunoreactive neurons. Our results indicate that accumulation of the inducible Hsp-72 in certain cell types may be part of a cytoprotective mechanism, which includes preservation of proteins like PrP(C).

Caspases, apoptosis, and Alzheimer disease: causation, correlation, and confusion

Extensive neuron loss occurs in Alzheimer disease (AD) brain and some authors have speculated that dysregulation of apoptotic death pathways is etiologically responsible for the disease. Apoptosis is regulated in mammalian cells by a family of cysteine proteases called caspases. At least 7 different caspases (caspases 1, 2, 3, 6, 8, 9, and 12) have been implicated in regulating neuronal cell death in response to amyloid beta (A beta) exposure in vitro, in animal models of neurodegenerative diseases, and in AD brain itself. Despite this seemingly impressive array of data implicating caspases and apoptosis as etiologic factors in AD, the direct involvement of caspase-dependent neuronal apoptosis in AD pathogenesis remains uncertain. Alternative explanations for some findings, contradictory experimental observations, and lack of morphologically convincing apoptotic neurons in the vast majority of AD brains has led to the revised hypothesis that apoptosis-associated molecular events cause neuronal dysfunction in the absence of, or prior to, neuronal death. Unfortunately, this new view renders the term "apoptosis-associated" functionally meaningless since it bears no relationship with apoptotic death and fails to focus scientific investigation on the molecular insults that trigger the "apoptosis-associated" response in AD neurons. On balance, an etiologic role for caspases in AD is far from proven. It remains possible, however, that caspase-dependent neuronal death contributes to AD neuron loss and thus, caspase inhibition offers some hope for extending AD neuron survival so that other agents, targeting upstream events, may delay or reverse primary AD pathology.

Beta-amyloid peptide expression is sufficient for myotube death: implications for human inclusion body myopathy

Inclusion body myositis (sIBM) is the most common disorder of skeletal muscle in aged humans. It shares biochemical features with Alzheimer's disease, including congophilic deposits, which are immunoreactive for beta-amyloid peptide (Abeta) and C'-terminal betaAPP epitopes. However, the etiology of myofiber loss and the role of intracellular Abeta in IBM is unknown. Here we report correlative evidence for apoptotic cell death in myofibers of IBM patients that exhibit pronounced Abeta deposition. HSV-1-mediated gene transfer of Abeta(42) into cultured C2C12 myotubes resulted in a 12.6-fold increase in dUTP-labeled and condensed nuclei over nonexpressing myotubes (P < 0.05). The C'-terminal betaAPP domain C99 also induced myotube apoptosis, but to a significantly lesser extent than Abeta. Apoptosis specific to Abeta-expressing myotubes was also demonstrated through DNA fragmentation, decreased mitochondrial function and the loss of membrane phospholipid polarity. Myotubes laden with Abeta(42), but not other transgene products, developed cytoplasmic inclusions consisting of fibrillar material. Furthermore, injection of normal mouse gastrocnemius muscle with HSV-encoding Abeta cDNA resulted in TUNEL-positive myofibers with pyknotic nuclei. We conclude that Abeta is sufficient to induce apoptosis in myofibers both in vivo and in vitro and suggest it may contribute to myofiber loss and muscle dysfunction in patients with IBM.

Mechanisms of cell death in primary cortical neurons and PC12 cells

Increasing evidence suggests that the regulation of neuronal cell death is complex. In this study we compared the neurotoxic effects of tumor necrosis factor-alpha (TNFalpha), nitric oxide, and thrombin on primary rat cortical cell cultures and the neuronal PC12 cell line. Release of lactate dehydrogenase (LDH) and the intracellular accumulation of nucleosomes were used as indicators of necrosis and apoptosis, respectively. There was significant LDH release in both neuronal cell types, however, the pattern of LDH release was variable and agonist-dependent. In response to the nitric oxide generator, sodium nitroprusside (SNP), cortical cells exhibited pronounced LDH release and dramatic morphologic changes, whereas in differentiated PC12 cells, TNFalpha evoked release of LDH with no associated morphologic changes. Both neuronal cell types, but not undifferentiated PC12 cells, responded to TNFalpha and thrombin with increased apoptosis. Caspase inhibition, but not antioxidant treatment, reduced nucleosome accumulation in primary cortical cells, but not in differentiated PC12 cells. In the differentiated PC12 cells, caspase inhibition reduced TNFalpha-mediated LDH release, but not nucleosome accumulation. These data suggest mechanisms involved in neuronal cell death utilize multiple pathways that vary depending on the neurotoxic insult and are also influenced by subtle differences among neuronal cell phenotypes.

CEP-1347/KT-7515, an inhibitor of SAPK/JNK pathway activation, promotes survival and blocks multiple events associated with Abeta-induced cortical neuron apoptosis

Although the mechanism of neuronal death in Alzheimer's disease (AD) has yet to be elucidated, a putative role for c-jun in this process has emerged. Thus, it was of interest to delineate signal transduction pathway(s) which regulate the transcriptional activity of c-jun, and relate these to alternate gene inductions and biochemical processes associated with beta-amyloid (Abeta) treatment. In this regard, the survival promoting activity of CEP-1347, an inhibitor of the stress-activated/c-jun N-terminal (SAPK/JNK) kinase pathway, was evaluated against Abeta-induced cortical neuron death in vitro. Moreover, CEP-1347 was used as a pharmacologic probe to associate multiple biochemical events with Abeta-induced activation of the SAPK/JNK pathway. CEP-1347 promoted survival and blocked Abeta-induced activation of JNK kinase (MKK4, also known as MEK-4, JNKK and SEK1) as well as other downstream events associated with JNK pathway activation. CEP-1347 also blocked Abeta-induction of cyclin D1 and DP5 genes and blocked Abeta-induced increases in cytoplasmic cytochrome c, caspase 3-like activity and calpain activation. The critical time window for cell death blockade by CEP-1347 resided within the peak of Abeta-induced MKK4 activation, thus defining this point as the most upstream event correlated to its survival-promoting activity. Together, these data link the SAPK/JNK pathway and multiple biochemical events associated with Abeta-induced neuronal death and further delineate the point of CEP-1347 interception within this signal transduction cascade.

Glyceraldehyde-3-phosphate dehydrogenase in neurodegeneration and apoptosis signaling

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a well-studied glycolytic enzyme that plays a key role in energy metabolism. GAPDH catalyzes the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate in the glycolytic pathway. As part of the conversion, GAPDH converts NAD+ to the high-energy electron carrier NADH. GAPDH has been referred to as a "housekeeping" protein and based on the view that GAPDH gene expression remains constant under changing cellular conditions, the levels of GAPDH mRNA have frequently been used to normalize northern blots. In recent years, that view has changed since GAPDH is now known to contribute to a number of diverse cellular functions unrelated to glycolysis. Normative functions of GAPDH now include nuclear RNA export, DNA replication, DNA repair, exocytotic membrane fusion, cytoskeletal organization and phosphotransferase activity. Pathologically, GAPDH has been implicated in apoptosis, neurodegenerative disease, prostate cancer and viral pathogenesis (see Sirover (1999) for a recent review of GAPDH functions). Most recently, it has been shown that GAPDH is a target for deprenyl related compounds (Carlile et al., 2000; Kragten et al., 1998) and may contribute to the neuroprotection offered by those compounds.

Changes in cytokines and neurotrophins in Parkinson's disease

Degeneration of the dopamine (DA) neurons of the substantia nigra pars compacta and the resulting loss of nerve terminals accompanied by DA deficiency in the striatum are responsible for most of the movement disturbances called parkinsonism, observed in Parkinson's disease (PD). One hypothesis of the cause of degeneration of the nigrostriatal DA neurons is that PD is caused by programmed cell death (apoptosis) due to increased levels of cytokines and/or decreased ones of neurotrophins. We and other workers found markedly increased levels of cytokines, such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-2, IL-4, IL-6, transforming growth factor (TFG)-alpha, TGF-beta1, and TGF-beta2, and decreased ones of neurotrophins, such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), in the nigrostriatal DA regions and ventricular and lumbar cerebrospinal fluid of PD patients. Furthermore, the levels of TNF-alpha receptor R1 (TNF-R1, p55), bcl-2, soluble Fas (sFas), and the activities of caspase-1 and caspase-3 were also elevated in the nigrostriatal DA regions in PD. In experimental animal models of PD, IL-1beta level was increased and NGF one decreased in the striatum of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonian mice, and TNF-alpha level was increased in the substantia nigra and striatum of the 6-hydroxydopamine (6OHDA)-injected side of hemiparkinsonian rats. L-DOPA alone or together with 6OHDA does not increase the level of TNF-alpha in the brain in vivo. Increased levels of proinflammatory cytokines, cytokine receptors and caspase activities, and reduced levels of neurotrophins in the nigrostriatal region in PD patients, and in MPTP- and 6OHDA-produced parkinsonian animals suggest increased immune reactivity and programmed cell death (apoptosis) of neuronal and/or glial cells. These data indicate the presence of such proapoptotic environment in the substantia nigra in PD that may induce increased vulnerability of neuronal or glial cells towards a variety of neurotoxic factors. The probable causative linkage among the increased levels of proinflammatory cytokines and the decreased levels of neurotrophins, candidate parkinsonism-producing neurotoxins such as isoquinoline neurotoxins (Review; Nagatsu, 1997), and the genetic susceptibility to toxic factors, remains for further investigation in the molecular mechanism of PD. The increased cytokine levels, decreased neurotrophin ones, and the possible immune response in the nigrostriatal region in PD indicate new neuroprotective therapy including nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin, immunosuppressive or immunophilin-binding drugs such as FK-506, and drugs increasing neurotrophins.

Sublethal concentrations of prion peptide PrP106-126 or the amyloid beta peptide of Alzheimer's disease activates expression of proapoptotic markers in primary cortical neurons

Neurodegenerative disorders such as prion diseases and Alzheimer's disease (AD) are characterized by neuronal dysfunction and accumulation of amyloidogenic protein. In vitro studies have demonstrated that these amyloidogenic proteins can induce cellular oxidative stress and therefore may contribute to the neuronal dysfunction observed in these illnesses. Although the neurotoxic pathways are not fully elucidated, recent studies in AD have demonstrated up-regulation of caspases in neurons treated with amyloid beta (Abeta) peptide, suggesting involvement of apoptotic processes. To examine the role of proapoptotic pathways in prion diseases we treated primary mouse cortical neurons with the toxic prion protein peptide PrP106-126 and measured caspase activation and annexin V binding. We found that PrP106-126 induced a rapid and marked elevation in caspase 3, 6, and 8-like activity in neuronal cultures. Increased annexin V binding was observed predominantly on cortical cell neurites in peptide-treated cultures. Interestingly, these effects were induced by sublethal (5-50 microM) or lethal (100-200 microM) concentrations of PrP106-126. Sublethal concentrations of PrP106-126 maintained elevated caspase activation for at least 10 days with no loss of cell viability. Abeta1-40 also up-regulated caspase 3 activity and annexin V binding at both sublethal (5 microM) and lethal (25 microM) concentrations. There were no changes to proapoptotic marker expression in cultures treated with scrambled PrP106-126 (200 microM) or Abeta1-28 (25 microM) peptides. These studies demonstrate that amyloidogenic peptides can induce prolonged activation of proapoptotic marker expression in cultured neurons even at sublethal concentrations. These effects could contribute to chronic neuronal dysfunction and increase susceptibility to additional metabolic insults in neurodegenerative disorders. If so, targeting of therapeutic strategies against neuronal caspase activation early in the disease course could be beneficial in AD and prion diseases.